Oxidačně - redukční reakce železa a oceli v roztocích a taveninách soustavy NaOH-H2O

Abstract

The thesis addresses electrochemical measurements using iron and iron oxide electrodes in concentrated solutions and melts of sodium hydroxide. The experimental apparatus was assembled for the electrochemical experiments by the temperature range 25 – 650 oC. Active surface of the experimental sondes was produced with micrometer movement of the electrode. Values of pH in the range of 14-17 were calculated from thermodynamic data for concentrated NaOH solutions for the temperature of 110 oC. The pH values were used for explanation of the received results of electrochemical experiments. Selected iron-based materials were used for experiments in 1M (4 % w/w) NaOH. A wire electrode of pure iron was prepared. Influence of scan rate on the electrochemical reactions of the wire electrode was studied in solution of NaOH with different concentrations (31, 50 and 69 % w/w). Nanostructured magnetite was electrochemically prepared on the surface of the wire electrode in the transpasivity region of oxygen and ferrates formation. Direct electrochemical reduction of the magnetite was studied in NaOH solutions with different concentrations. Influence of the electrochemically produced hydrogen on the reduction of magnetite was investigated. Based on these experimental data, several differences of reduction mechanism in the solutions having concentration of 31 and 50 % were found. A method for “in situ” determination of H2O and Na2O was designed in acidic and basic melts of NaOH at temperature of 400 oC. A mechanism of water bonds was studied in acidic melts of NaOH by mathematical modeling. Possibilities of electrochemical descaling quality determination of austenitic stainless steel AISI 304 were solved as well. Simply, easy and fastened voltammetric and electrochemical impedance methods was suggested for this determination in 1M solution of NaOH.